Vehicle Systems, Brakes, and Pre-Trip Fundamentals
What this domain tests
This domain tests basic system knowledge and brake checks. It includes air-brake warning systems, spring brakes, cooling and electrical checks, and when a vehicle must be placed out of service.
Core rules
- Check oil, coolant, belts, hoses, battery, lights, tires, and brake components before driving.
- Know the low-air warning: it must activate before pressure drops below 60 psi. Spring brakes apply automatically at roughly 20 to 45 psi.
- Test the parking brake, service brake, and ABS warning light. Drain air tanks to remove moisture.
- Do not rely on ABS to correct poor braking; ABS prevents wheel lockup, not excessive speed.
Worked example
During a pre-trip air-brake test, the low-pressure warning does not sound until 50 psi. The vehicle fails the check because the warning must occur before 60 psi. The driver should not move the vehicle until the defect is repaired.
Traps
Assuming ABS means the brakes need no adjustment, ignoring a coolant leak, and skipping air-tank draining are common mistakes. A warning that comes on too late is a defect, not a minor annoyance.